An echo is a long delay telephone circuit, such as a satellite communication circuit or the like, causes marked degradation of the speech quality. An echo suppressor now in use effectively suppresses an echo but has a defect such that degradation of the speech quality, such as speech interruptions, echos during overlapped talking, etc., is in principle unavoidable; therefore, an echo canceller gets much attention as a new echo suppressor. The principle of the echo canceller is to estimate the transmission characteristic of an echo path by the use of a received signal and an echo signal, to produce an echo replica on the basis of the estimation result and to subtract it from the true echo signal, thereby cancelling an echo.
The algorithm for the estimation of the transmission characteristic of the echo path in the conventional echo canceller is mainly based on a learning identification method; but, with this system, in a case of using a voice signal as the input signal, the convergence time is long so that the cancelled amount of an echo signal is insufficient due to high correlation in comparison with those in a case of using white noise as the input.